1. Field
Example embodiments relate to a digital image stabilization method, and more particularly, to a digital image stabilization method capable of correcting an image by using homography to indicate correlations between two image frames used for a conventional panorama image if the image is distorted or moves in a horizontal/vertical direction due to camera shake.
2. Description of the Related Art
The quality and resolution of image sensors based on a CMOS process has recently increased, allowing the production of inexpensive digital cameras. Digital cameras are becoming increasingly miniaturized due to the intrinsic characteristics of CMOS image sensors, and are thus being applied to portable information terminals such as PDAs, cellular phones, smart phones, etc. An extension of a wired/wireless communication network makes it possible to capture, process, and transmit desired images at any time and place.
An increase in the use of mobile communication terminals involves image scattering due to a camera shake. Therefore, it may be necessary to correct motion such as camera shake in order to stabilize images. A gyro sensor or an image processor may be used to correct the motion of images.
The image processor may be used to compare a current frame and a previous frame and correct the motion of an image according to the comparison result. An image memory of a digital camera for storing the previous frame may be used to calculate the change between the current frame and the previous frame using a motion vector. The image processor may be widely used for small digital cameras or mobile communication terminals since it may not require mechanical or physical elements and may be easier to employ owing to its simple structure.
FIG. 1 is a flowchart illustrating a conventional image motion correction method that may use an image processor. An image projection method may be used to calculate a motion vector of an image and correct the image using the motion vector.
Referring to FIG. 1, if a camera system in the conventional art operates and a motion correction function starts, the resolution for the correction of motion is determined (Operation 110). A motion displacement is considered to determine the resolution lower than a whole resolution. A plurality of window regions for calculating the motion vector are established (Operation 120). Row/column lines to be sampled are established in each window region (Operation 130).
Thereafter, data is extracted from the row/column lines (Operation 140), and compared with corresponding data extracted from a previous image frame (Operation 150). The motion vector is calculated based on the comparison result (Operation 160). A start point moves by the motion vector (Operation 170). A current image frame having the corrected motion is output (Operation 180).
As described above, the conventional image motion correction method calculates the motion vector using the sampled row/column line data in a definite window region of the current image frame. If the image shakes, the image may move only in a horizontal or vertical direction. The motion vector is calculated on the assumption that the horizontal or vertical motion has the same magnitude over the whole image.
FIG. 2 illustrates image variations in the conventional art, due to camera shake. Referring to FIG. 2, a center image shows no camera movement. An upper image shows upward camera movement. A lower image shows downward camera movement. A left image leftward camera movement. A right image shows rightward camera movement.
When the camera moves upward, the image may be elongated. When the camera moves downward, the image may be compressed. When the camera moves left, the image leans to the left. When the camera moves right, the image leans to the right.
In particular, a conventional CMOS image sensor used with a rolling shutter does not simultaneously output optical signals from a plurality of optical elements for receiving data of a single frame to a floating diffusion (FD) node, but outputs them in row units, which greatly increases the image distortion when the camera shakes.